1. Field of the Invention
The present invention relates to an electroacoustic converter, and more particularly is directed to an improvement on an electroacoustic converter such as a loudspeaker or a microphone having a dome-like diaphragm.
2. Related Background Art
A conventional dome-like loudspeaker has a cross-section as shown in FIG. 1. The magnetic circuit is constructed of a center pole 38, a yoke 39, a magnet 301, and a top plate 34. A magnetic gap is formed between the outer wall of the center pole 38 and the inner wall of the top plate 34. A known diaphragm system is constructed of a unit body of a dome-like diaphragm 30 and a coil bobbin section 35 integrally formed with the diaphragm 30 and having a voice coil wound thereabout, and a curved edge section 31 attached to the unit body. Another is constructed of a unit body of a dome-like diaphragm 30 and an edge section 31, and a coil bobbin attached to the unit body. In such diaphragm system, the coil bobbin section 35 together with the voice coil 36 is properly inserted in the magnetic gap, and the outer periphery of the edge section 31 is sandwiched, at a supporting step formed at the inner wall of the top plate 34, between edge supporting members 33 having almost no resilience. The diaphragm system is fixedly supported by pressing the edge pressing members 33 by the tip of a frame 302. Conventionally, a jig 304 shown in FIG. 2A has been used to precisely define a magnetic gap during an assembly process of a loudspeaker. The jig is formed with a tubular section 305 whose thickness corresponds the magnetic gap, and the top plate 34 is assembled by covering the tubular section 305 on the center pole 38. The magnetic circuit elements 34, 301, and 39 are coupled together with adhesive agent, and after drying and hardening of the adhesive agent, the jig 304 is removed to complete the magnetic circuit as shown in FIG. 2B.
Conventional magnetic circuits described above have required a jig for formation of an adequate magnetic gap. In addition, to remove the jig after hardening of the adhesive agent, it is necessary to provide some clearances g between the center pole 38 and the tubular section 305 and between the tubular section 305 and the top plate 34, as particularly shown in the enlarged cross section of FIG. 2C. As a result, there are associated with some problems that it is difficult to obtain a uniform gap, and that the clearance g must necessarily be incorporated to define the gap distance. This clearance g degrades particularly the performance of a high frequency loudspeaker. Further, use of an adhesive agent for bonding each magnetic circuit element requires a time for drying and hardening, thereby resulting in a loss in time during an assembly process.
A dome-like loudspeaker is constructed in such a way that the outer periphery or brim 32 of the edge section 31 extended from the diaphragm 30 is sandwiched between the ring-like edge supporting members 33 which are bonded to the top plate 34 for support of the diaphragm system. With such construction, the lead wires 37 of the coil 36 wound about the coil bobbin section 35 are drawn to the side of the edge section 31 and sandwiched between the edge supporting members 33. Generally, a middle- and high-frequency dome-like loudspeaker of this type is small in dimension and has a narrow edge section. Therefore, the lead wires 37 are carefully guided so as not to contact the edge section 31 or the top plate 34, and carefully sandwiched so as not to cut or make short-circuited. Such wiring operation of the lead lines 37 is very difficult and complicated at a limited working space, thus causing a low productivity and a low yield.
Also, the diaphragm system with a conventional supporting structure moves using the inner wall corners of the edge supporting members as a fixed point. Therefore, a substantial stress may be applied to the edge section, and a deteriorated sound quality may occur due to such a large distortion at about fo.